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United States Patent |
5,728,104
|
Trotta
|
March 17, 1998
|
Method of catheter balloon manufacture and use
Abstract
A catheter balloon is prepared for inflation, and the balloon is inflated
by the following process. At least a portion of an elastic, thermoplastic
tube is radially stretched until the radially stretched tube portion
exhibits a desired increase in molecular orientation. The stretching
conditions, such as selective heating, preferably cause a central section
of the stretched tube portion to have less wall thickness than end
sections of the tube portion. At least part of the tube portion may be
longitudinally stretched relative to the tube, to create a desired biaxial
molecular orientation. Thereafter, the tube portion is optionally placed
into a stent, the tube portion being part of a catheter. The tube portion
is inserted into a patient to position the stent and tube portion at a
desired position, such as a location in the coronary artery. After
positioning of the tube portion and stent, the lumen of the tube portion
is pressurized to cause radial expansion of the tube portion within the
patient, with a central section of the tube portion expanding first.
Inventors:
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Trotta; Thomas N. (Miami, FL)
|
Assignee:
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Cordis Corporation (Miami Lakes, FL)
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Appl. No.:
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795248 |
Filed:
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February 10, 1997 |
Current U.S. Class: |
606/108; 606/194 |
Intern'l Class: |
A61F 011/00 |
Field of Search: |
606/108,194,191,192,198
604/96,97,98
|
References Cited
U.S. Patent Documents
5156612 | Oct., 1992 | Pinchuk et al.
| |
5449371 | Sep., 1995 | Pinchuk et al.
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5490838 | Feb., 1996 | Miller.
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5569296 | Oct., 1996 | Marin et al. | 606/194.
|
5609605 | Mar., 1997 | Marshall et al. | 606/191.
|
5645560 | Jul., 1997 | Crocker et al. | 606/108.
|
Primary Examiner: Buiz; Michael
Assistant Examiner: Truong; Kevin
Attorney, Agent or Firm: Gerstman Ellis & McMillin, Ltd.
Parent Case Text
This application is a division of U.S. application Ser. No. 08/614,399,
filed Mar. 12, 1996, now U.S. Pat. No. 5,643,279.
Claims
That which is claimed:
1. A catheter which comprises a tubular catheter body, an inflation lumen,
and a tubular plastic distal portion having a bore communicating with said
catheter inflation lumen, said tubular plastic distal portion being made
of a plastic material which, when introduced into a patient and inflated,
stretches longitudinally and radially to undergo molecular orientation on
stretching; said plastic distal portion being surrounded by a radially
expansible tubular stent and having an outer wall in its uninflated
condition that is smooth and free of folds.
2. The catheter of claim 1 in which said plastic distal portion comprises a
formulation selected from the group consisting of nylon and polyethylene.
3. The catheter of claim 1 in which said distal portion has a maximum
diameter prior to inflation of no more than twice the minimum diameter of
an adjacent tubing of said catheter.
4. A catheter which comprises a tubular catheter body, an inflation lumen,
and a tubular plastic distal portion having a bore communicating with said
catheter inflation lumen, said tubular plastic distal portion comprising
an elongated, inflatable, longitudinally and radially stretchable catheter
balloon having a central portion and end portions, said central portion
having a lesser wall thickness than said end portions to cause the central
portion of said balloon to inflate more rapidly than said end portions.
5. The catheter of claim 4 in which said balloon is surrounded by a
radially, expansible stent, said stent being centered on said balloon
whereby, upon balloon inflation, a central portion of said stent inflates
prior to end portions of said stent, driven by the inflation of said
balloon.
6. The catheter of claim 5 in which said balloon comprises a material
having sufficient crystallinity to undergo molecular orientation on
stretching.
7. The catheter of claim 4 in which said tubular plastic distal portion
comprises a formulation selected from the group consisting of nylon and
polyethylene.
8. The catheter of claim 4 in which said tubular plastic distal portion has
a maximum diameter prior to inflation of no more than twice the minimum
diameter of an adjacent tubing of said catheter, said tubular plastic
distal portion having an outer wall that is smooth and free of folds.
Description
BACKGROUND OF THE INVENTION
In Miller U.S. patent application Ser. No. 08/294,659 entitled of "Method
of Inserting a Balloon Catheter", now U.S. Pat. No. 5,490,838 a balloon
catheter is disclosed in which the balloon in its non-inflated
configuration has a smooth, cylindrical wall, and is no greater in
diameter than the remainder of the catheter. The balloon, in its original
form, is a tube made of an elastically expandable, work-hardenable
plastic, such as known forms of nylon or polyethylene (polyethylene
terephalate).
A stated advantage of such a balloon lies on the fact that as the balloon
expands with increasing internal pressure, there is a pressure range which
the work-hardening primarily takes place which has an effect of reducing
or eliminating the expansion of the balloon with increasing pressure.
Thus, if a doctor expands the balloon within a patient to this pressure
range, he or she can know with confidence that the balloon diameter is no
greater than a predetermined maximum diameter, without the need for a
direct observation.
Furthermore, a popular surgical procedure for preventing restenosis in
arteries utilizes a catheter dilatation balloon which is surrounded by an
expandable tubular stent, for example a wire stent, or an apertured tube
stent of the type sold by the Johnson and Johnson Corporation. The balloon
and stent are positioned as desired within an artery or other vessel lumen
of a patient. Then the balloon is expanded, to expand the stent to a
desired configuration. It is desirable to avoid overexpansion from such a
balloon as the stent is being expanded.
Conventional arterial dilatation balloons are flexible but not very
stretchable, so that they are initially wrapped up in a folded
configuration. Disadvantage has been encountered when these balloons are
used with stents because of the possibility that, due to nonuniformities
in the unfolding, certain portions of the stent become more greatly
outwardly pressurized than other portions.
Also, if a stent balloon tends to expand one end or the other first, rather
than first in the middle while in the process of expanding the stent, the
stent can be driven off the balloon by such asymmetric expansion, so that
the stent becomes only partially expanded. This of course can be a great
problem during surgery, and may result in the stent becoming positioned
improperly in the expanded configuration.
In accordance with this invention, a catheter balloon is provided which can
be very narrow prior to inflation, and which can inflate in a
circumferentially uniform manner, which is predictably dependent on the
inflation pressure, for optimum implantation of stents within the body,
and also for other medical uses which are customary for catheter balloons.
DESCRIPTION OF THE INVENTION
In accordance with this invention, a method is provided for preparing a
catheter balloon for inflation and for inflating the balloon, which
comprises:
(A) A portion of a stretchable tube capable of undergoing molecular
orientation is radially stretched until said radially stretched tube
portion exhibits a desired increase in molecular orientation. The term
"stretchable" or "stretched" as used herein implies that the tube tends to
not shrink back to its original configuration after such stretching, but
it spontaneously remains substantially in its stretched configuration,
apart from special measures such as heating to activate plastic memory or
the like.
(B) At least part of the above tube portion is longitudinally stretched to
create a desired increase in molecular orientation longitudinally relative
to the tube.
(C) Thereafter, the tube portion is inserted as part of a catheter into a
patient, for example, into a coronary artery. A lumen of the tube portion
is pressurized to cause radial expansion of the tube portion within the
patient, for advantages as described in the cited Miller application, and
also as described below.
Further in accordance with this invention, a balloon may be made from
thermoplastic tube by radially stretching at least a portion of the
thermoplastic tube while causing a central section of the tube portion to
stretch to a lesser wall thickness than end sections of the tube portion.
Preferably, one then longitudinally stretches at least part of the tube
portion to reduce the diameter of the catheter balloon prepared from the
thermoplastic tube prior to inflation. Also, when the thermoplastic used
can be significantly oriented on a molecular basis, the balloon can be
biaxially oriented by the radial stretching step and the longitudinal
stretching step. This characteristic of many plastics is a well-known and
understood property.
Thereafter one can insert the tube portion as part of a catheter into a
patient, pressurizing the lumen of the tube by an amount sufficient to
cause radial expansion of the tube portion to take place within the
patient while the tube portion is surrounded by an expansible stent for
implantation. Because, by this invention a central section of the tube
portion preferably may be of lesser wall thickness than end sections of
the same tube portion, at least initially more radial expansion of the
central section of the tube portion takes place than end sections thereof.
Thus, a central portion of the stent can be expanded first within the
patient, with the entire stent being subsequently expanded by further
inflation of the balloon formed from the tube portion, to provide
spontaneous assurance that the stent will not shift on the balloon during
the inflation of the balloon and expansion of the stent. The balloon's
radial expansion tends to begin in the middle, and spreads to the ends.
Thus, a surrounding, centered stent is not pushed off of the balloon, as
may be the case if the balloon expands at one end first.
Also, as described in the previously cited patent application, the
balloon's radial expansion may cause molecular orientation of the tube
portion, resulting in work-hardening, so that, at a predetermined pressure
range, the diameter of the balloon formed from the tube portion is
relatively constant and known.
If desired, prior to step A above, at least some of the plastic tube
portion may be longitudinally stretched to create increased longitudinal
molecular orientation. The details of this and the above stretching steps
may be performed as described in Pinchuk et al. U.S. Pat. No. 5,156,612,
with the exception of that, contrary to the teachings of that patent, the
final balloon inflation step disclosed therein takes place within the
patient, and not as a process step in the manufacturing of the balloon and
catheter.
Numerous, different plastic formulations undergo molecular orientation, so
as to be useable to manufacture plastic tubes for processing in accordance
with this invention. Specifically, the balloon-forming plastic tube may be
made of stretchable forms of nylon and polyethylene polymers or copolymers
(such as poly(ethylene-propylene) which exhibit desired properties for use
herein. Specifically nylons 612, 11, and 12 may be used, typically of a
relative solution viscosity of about 1.6 to 2.2 as determined by The
International Standards Organization Test ISO 307/DIN 53 727, with
m-creosol as a solvent, employing a concentration of 0.5 gm. of nylon 12
per 100 ml. of M-creosol. With nylon 12, a relative solution viscosity of
about 2.1 is preferred.
The tube portion which is to be inserted into the patient preferably has a
diameter prior to said pressurizing of step (C) above within the patient
of no more than about twice the minimum diameter of adjacent tubing of the
catheter. Preferably, the pre-expanded tube portion discussed above may
have a diameter of less than 50 percent over the minimum diameter of
adjacent catheter tubing, and is preferably of substantially equal
diameter to such catheter tubing, so that the tube portion which is to
become the balloon may slide easily along with the rest of the catheter
tubing into a non-expanded, tubular stent, and into a blood vessel or body
lumen without difficulty.
Also, the formed balloon preferably has an outer wall that is smooth and
free of folds, contrary to the presently conventional catheter dilatation
balloons for angioplasty and the like. This is rendered possible by the
stretching capability of the catheter tube portion to form the desired
balloon, while at the same time one or more desired maximum balloon
expansion diameters (one larger than the other) may optionally be achieved
at predetermined pressure ranges in the manner described in the cited
Miller patent application.
It is also preferred for the length of the plastic portion which is
radially stretched in step (A) above to be less than and included in the
length of the plastic portion which is longitudinally stretched in step
(B). The stent, when applied to the balloon described herein, may be
preferably longitudinally centered on the length of the plastic portion
which is radially stretched in step (A). As described above, a central
portion of the balloon of this invention preferably tends to expand first,
causing a central portion of the stent to expand first relative to end
portions thereof. Then, the end parts of the plastic tube portion
longitudinally stretched will expand also, to cause end portions of the
stent to expand as well. However, by this technique the stent will not
slide off the balloon, avoiding the problem which has been encountered in
some surgical procedures.
Other orientable thermoplastic materials may be used as well as nylon and
polyethylene as orientable thermoplastics for use as a catheter balloon in
accordance with this invention. They may be selected from other materials
such as polyamide block copolymers, polyamide copolymers, amorphous
polyamides, and polyester copolymers, for example.
In each of steps (A) and (B) above, the molecular orientation of the tube
is accomplished by applying a force greater than the material's yield
point to cause stretching, but less that its ultimate tensile strength. In
the radial expansion or stretching step (A), control of the location of
the material which is stretched may be made by the local application of
heat, to lower the yield point of the desired area where radial expansion
is to be achieved. A gradation of heat applied can cause the middle of the
newly-formed balloon to stretch more than end portions and thus to have a
lower wall thickness. Alternatively the tube may initially have a thinner
central portion.
The tubing section may be re-oriented sequentially by longitudinal
stretching, followed by radial pressurized stretching, without a
significant loss of shape-forming capability. It may be desirable in some
cases to sequentially repeat the respective steps (A) and (B) several
times, as may be desired.
DESCRIPTION OF DRAWINGS
In the drawings, FIG. 1 is a perspective view of a portion of a plastic
tube, or if desired, an entire length of tube, which is to be biaxially
oriented in accordance with this invention for the formation of a catheter
balloon;
FIG. 2 is a perspective view of the tube portion of FIG. 1 after it has
been longitudinally stretched in accordance with a preferred embodiment of
this invention;
FIG. 3 is a perspective view of the plastic tube portion of FIG. 2 after a
smaller portion thereof has been radially stretched in accordance with
step (A) as described above;
FIG. 4 is a perspective view of the tube of FIG. 3 after it has been again
longitudinally stretched in accordance with step (B) as described above,
and showing a stent placed thereon for purposes of illustration; and
FIG. 5 is a fragmentary, perspective view of a catheter which incorporates
the plastic tube balloon of this invention, which is attached onto the end
of the catheter and inserted into a coronary artery, schematically showing
the stent surrounding the balloon after partial inflation thereof, where a
central portion of the stent and balloon are inflated more than end
portions thereof;
DESCRIPTION OF SPECIFIC EMBODIMENTS
Referring to the drawings, a method for preparing a catheter balloon for
inflation and for inflating the balloon is illustrated. A plastic tube 10
is provided in accordance with FIG. 1, the plastic material of the tube
preferably having the capability to undergo biaxial orientation. For
example, a relatively low crystalline nylon 12 may be used to manufacture
tube 10.
Tube 10 may be either bonded to a catheter tube 12 during the manufacturing
steps of the method of this invention, or subsequently, prior to use of
expanding the balloon within the patient. Alternatively, tube 10 may be
integrally extruded with catheter tube 12.
As a first preferred step, especially for use with nylons 612, 11 or 12,
tube 10 is longitudinally stretched as in FIG. 2 to create a desired,
increased, longitudinal molecular orientation relative to the tube, as
illustrated by tube 10a, which comprises the stretched portion of tube 10
after the first step of processing. Specific conditions for this
processing may vary, depending upon the materials, but are generally
familiar to those skilled in the art of the molecular orientation of
plastics. Also, the pertinent disclosures of Pinchuk et al. U.S. Pat. No.
5,156,612 may be utilized in developing a specific process, the
disclosures of that patent being incorporated by reference herein.
FIG. 3 corresponds to method step (A) above, as previously discussed.
Tubing 10a from FIG. 2 may have a portion thereof heated by a conventional
heater 14, so that the yield point of the heated plastic drops relative to
the remaining plastic of tube 10b, which is tube 10a as modified by the
processing step of FIG. 3. Then, lumen 16 of the tube may be pressurized
in a mold 17 to restrict balloon expansion and to cause a preliminary
balloon 18 to form. A desired, increased radial expansion and molecular
orientation is provided to balloon 18, resulting in at least a degree of
biaxial orientation to balloon 18.
Heater 14 may have a central section 19 that heats a central portion 18a of
balloon 18 slightly more than the terminal portions 18b of the balloon.
Thus, the wall thickness of balloon 18a may be slightly reduced relative
to the wall thickness of balloon end portions 18b. Mold 17 may have an
appropriate outward bulge if desired to accommodate the added stretching
and thinning of the walls of central section 18a. For example, the wall
thickness of central catheter balloon portion 18a may be approximately
0.0003 to 0.0015 inch while the wall thicknesses of end portions 18b may
be approximately 0.0002 inch thicker than the wall thickness of portion
18a after the expansion of FIG. 3 and prior to the processing of FIG. 4.
Thereafter, the step of FIG. 4 may be performed, which is step (B) as
previously described, in which tube portion 10b is longitudinally
stretched to form tube portion 10c as shown in FIG. 4. Balloon 18 exhibits
a reduction in diameter, with the prior internal pressurizing within the
tube being released to facilitate the desired longitudinal stretching, for
further longitudinal molecular orientation of the plastic tube.
Preferably, the balloon formed has an equal diameter at its opposed ends.
Then, contrary to the cited Pinchuk et al. patent, the catheter is ready
for medical use except for the known and necessary steps such as
sterilization, adding components, and the like. Catheter portion 10c may
be attached to the rest of the catheter if that has not been previously
done.
Referring to FIG. 5, catheter 12 is shown carrying plastic tube portion
10c. Lumen 16 communicates with an inflation lumen 17 of the rest of
catheter 12. Tube portion has a closed, distal end 19 in this embodiment.
However, if desired, multiple lumen catheters may be provided in which at
least one lumen passes through end 19 while the inflation lumen terminates
in the area of balloon 18.
Balloon 18 carries a tubular, crossing-wire, or apertured-tube, expansible
stent 22 of conventional design, with the catheter 12 and stent 22 being
shown to be occupying an artery 24 of a patient. Stent 22 is placed about
plastic tube portion 10c while in the collapsed configuration of FIG. 4.
Then, when balloon 18 and stent 22 have been positioned at the proper
place in artery 24, the lumen of catheter 10c is inflated to a
predetermined pressure. Balloon 18 expands as shown in FIG. 5, with the
middle of balloon portion 18 being centrally located within stent 22. The
center of balloon 18 expands first, since it is of slightly reduced wall
thickness, expanding a central portion 26 of stent 22 outwardly more
rapidly than the expansion of the end portions 28 of the stent. This
causes the stent to remain in position on the balloon, and not to be
forced off the balloon by its expansion, as may take place when expansion
begins at an end portion of the stent. Following this, end portions 30 of
the balloon may be inflated more than shown, to drive added portions of
the stent 22 radially outwardly into a fully expanded configuration, as
shown in dotted lines.
Following the desired expansion of the stent, the lumen of tubing 10c can
be depressurized, causing balloon 18 to collapse, so that catheter 20 and
its distal tube section 10c may be withdrawn, leaving the expanded stent
22 behind in the artery.
Because of the absence of folds in the balloon, which expands as a tube in
a stretching manner with a thinning sidewall, the stent may be expanded
with more uniform circumferential pressures against all of its inner
surfaces (disregarding the issue of central preexpansion of the balloon).
This results in better stent placement than can often be achieved with
catheter balloons of the prior art. Also, balloon 18 can cease its
expansion at a predetermined diameter in a predetermined elevated pressure
range due to work hardening, which increases the assurance that the
balloon will not be over inflated.
The above has been offered for illustrative purposes only, and is not
intended to limit the scope of the invention of this application, which is
as defined in the claims below.
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